Digital printers employing an electrophotographic process have lately become widely used in the production printing field. The digital printers employing the electrophotographic process are thus required to offer higher image quality and greater reliability. In particular, the digital printers employing the electrophotographic process are required to offer, for example, improved fine line reproducibility, improved character reproducibility (e.g., improved reproducibility of characters of minute sizes equivalent to 2 to 3 points), prevention of characters from becoming broader due to the electrophotographic process, and improved color shift correction accuracy.
In order to achieve the higher image quality, the digital printer employing the electrophotographic process includes an image processor that corrects image data through image processing. The image processor performs image processing for, for example, multi-bit data having a high resolution, for example, of 1200 dots per inch (dpi) or 2400 dpi.
The digital printer employing the electrophotographic process further includes, for example, a photoconductor drum, a light source, a polygon mirror, and a scanning optical system. Specifically, the photoconductor drum has a surface that functions as a scanned surface having photosensitivity; the light source emits a laser beam; the polygon mirror deflects the laser beam from the light source; and the scanning optical system guides the laser beam deflected by the polygon mirror onto the surface (scanned surface) of the photoconductor drum. The digital printer employing the electrophotographic process modulates luminous flux emitted from the light source according to the image data to thereby irradiate the scanned surface with the luminous flux from the light source. By then scanning the scanned surface with the luminous flux, the digital printer employing the electrophotographic process forms an electrostatic latent image on the photoconductor drum according to the image data.
The digital printer employing the electrophotographic process having the configuration as described above includes as the light source a laser diode array (LDA), a vertical-cavity surface-emitting laser (VCSEL), or other element having a plurality of light emitting points. This arrangement enables the digital printer employing the electrophotographic process to form an electrostatic latent image having a resolution higher than image data of 1200 dpi, specifically, a 2400-dpi or 4800-dpi electrostatic latent image.
Patent Literatures 1 and 2 each disclose a technique in which, through processing performed by an image processor, blank portions in the image are detected and blank lines are extended or pixels around blank characters are corrected. Reverse characters (drawn in white on a black background) are thereby prevented from being collapsed and improved character reproducibility is achieved. Patent Literature 3 discloses a technique in which a controller simultaneously performs both thinning and smoothing using template matching with multi-valued data.
Processing of a high-density image involves a problem in data transfer from the image processor to a light source drive circuit downstream thereof. If the image processor processes multi-bit data images with a resolution, for example, of 2400 dpi or 4800 dpi, the degree of freedom in image processing is enhanced and reproducibility of 1200-dpi characters and lines of minute sizes can be improved. High-density image processing, however, requires an enormous amount of data to be transferred from the image processor to the downstream light source drive circuit, which restricts a productivity improvement rate.
Performing all processing for improving reproducibility of the minute characters and lines with the upstream image processor makes the processing complicated and places a heavier load on the image processor.